An experimental investigation of nonequilibrium effects in wall-confined argon plasma arcs

Abstract

This paper deals with thermal equilibrium between the particles in argon plasma arcs. The current limit for LTE is experimentally defined as a function of the pressure. Plasma parameters were spectroscopically determined. In particular, the electron temperature and heavy particle temperature were measured. The electron temperature was determined from an absolute continuum radiation strength. Two temperatures were obtained for the heavy particles, one of which was determined from the Doppler component of the H, line when argon gas seeded with hydrogen was used. The second was obtained through a kinetic formula using the measured density and temperature of the electron. The results show that the electrons did not equilibrate with the heavy particles at low currents and pressures. The limit value of the current for LTE increased with decreasing gas pressure. It is shown, furthermore, that the measured field strength of the arc was remarkably lower than those calculated at currents less than the above limits.

A collisional-radiative model applicable to argon discharges over a wide range of conditions. III. Application to atmospheric and subatmospheric pressure arcs

“…In table 1 we give the basic data (I) characterising the excited effective levels studied in this paper. They include the all excited states investigated in the above mentioned experimental works of Nick et a1 (1984), Shumaker and Popenoe (1972), and Shindo and Imazu (1980).…”

“…In figure 5 we give the values of n,/gn measured by Shindo and Imazu (1980) for the all 4s states as well states on the axis of an argon wall-stabilised arc of 6 mm diameter at the pressure of 500 Torr. As shown, the populations approximate to a Boltzmann distribution at the indicated (Shindo and Imazu 1980) excitation temperature of 12 000 K within the probable error.…”

“…Valuable results contributing to the elucidation of the non-equilibrium effects and the population mechanisms in argon arc discharges have been obtained in recent years by Bacri and Gomes (1978), Shindo and Imazu (1980), GomCs (1983), Nick et a1 (1984), Timmermans et a1 (1985) and by Cram et a1 (1988).…”

“…The main aim of the present paper is to check the reliability of our extensive CR model under the conditions in the atmospheric pressure arc, studied experimentally by Nick et a1 (1984), and in the subatmospheric pressure arcs, investigated experimentally by Shumaker and Popenoe (1972) and by Shindo and Imam (1980). Further motivation for this study was provided by our interest in understanding the population mechanisms leading to the departures from the LTE state in the axial regions of these discharges (Nick et a1 1984, Shumaker andPopenoe 1972) and in the question of equivalence between the electron kinetic temperature and an excitation temperature spectroscopically determined in them (Shindo andImam 1980, Eddy 1985). The mentioned experimental works have been chosen because the set of the discharge parameters measured is consistent with the input parameters of our CR model.…”

Calcul de propriétés thermodynamiques et des coefficients de transport dans un plasma Ar-O2 en non-équilibre thermodynamique et à la pression atmosphérique

“…On emploie alors des méthodes de calcul désormais classiques : minimisation de l'énergie libre pour la détermination de la composition du gaz plasmagène et pour les propriétés de transport les méthodes décrites dans les références [1-4] à la condition que les sections efficaces de collision élastique ou les potentiels d'interaction entre les diverses espèces présentes dans le système soient connus. Cette hypothèse d'ETL est cependant souvent mise en défaut; en effet, de nombreuses études expérimentales [5] à [8] montrent, en particulier, que dans des plasmas en extinction et au voisinage d'une surface solide ou liquide, dans la couche limite, l'énergie cinétique moyenne des électrons est, le plus souvent, supé-rieure à celles des particules lourdes. Il y a alors redistribution des vitesses pour ces deux sous-ensembles de particules, au voisinage de deux maxwelliennes, l'une à la température Te pour les électrons et l'autre à la température Th pour les particules lourdes.…”